Li og B samsætur í íslensku storkubergi og jarðhitavökva - verkefni lokið

Fréttatilkynning verkefnisstjóra

6.7.2023

The project had three major parts. In the first part of the project, the ratio of the abundance of two Boron isotopes was measured in a large suite of Icelandic lavas that comprehensively spanned the chemical and spatial distribution of
lavas in Iceland. Because the ratio of boron isotopes is only changes on the Earth’s surface, variations in the ratio detect the presence of materials previously at the surface. The project identified correlations between boron isotopes and several geochemical indicators that detect previously subducted oceanic crust beneath Iceland. This subducted crust is then melted to form Icelandic basalt along with other plume materials. For the first time, boron isotopes were further able to place constraints on the history of heating and volatile loss within the subducted oceanic material. This shows that the Icelandic mantle plume dredges and remelts previously subducted materials, confirming observations from other In the second part of the project, the ratios of lithium isotopes were measured in a similar suite of lavas to the boron isotope study. Like boron isotopes, lithium isotopes are fractionated at Earth surface, but they can also be fractionated deep within the Earth. By combining the lithium isotope dataset with previously measured Helium isotope ratio data, it became clear that the variability in lithium isotopes was more likely related to deep magmatic processes rather than shallow processes. Geochemical modelling of the problem showed that deep magmatic processes likely play a much greater role in changing lithium isotopes in lavas on Earth with major implications for the interpretation of lithium isotope signatures in basalt lavas globally. In the third, and last part, stable isotopes from the 2021 Fagradalsfjall eruption and from Bardarbunga volcano were measured in order to investigate the origin of low oxygen isotope ratios in Icelandic lavas. Both studies suggested that a low oxygen isotope component exists within the Icelandic mantle source, indicating that low oxygen isotope ratios may be an intrinsic signature of materials at the core-mantle boundary.

∙ Information on how the results will be applied
The results of the project are, or will be, published in high-impact international journals.

∙ A list of the project’s outputs
Marshall, E.W., Ranta, E., Halldórsson, S.A., Caracciolo, A., Bali, E., Jeon, H., Whitehouse,
M.J., Barnes, J.D., Stefánsson, A., 2022. Boron isotope evidence for devolatilized and
rehydrated recycled materials in the Icelandic mantle source. Earth Planet. Sci. Lett. 577,
117229. https://doi.org/10.1016/j.epsl.2021.117229

Halldórsson, S.A., Marshall, E.W., Caracciolo, A., Matthews, S., Bali, E., Rasmussen, M.B.,
Ranta, E., Robin, J.G., Guðfinnsson, G.H., Sigmarsson, O., Maclennan, J., Jackson,
M.G., Whitehouse, M.J., Jeon, H., van der Meer, Q.H.A., Mibei, G.K., Kalliokoski,
M.H., Repczynska, M.M., Rúnarsdóttir, R.H., Sigurðsson, G., Pfeffer, M.A., Scott, S.W.,
Kjartansdóttir, R., Kleine, B.I., Oppenheimer, C., Aiuppa, A., Ilyinskaya, E., Bitetto, M.,
Giudice, G., Stefánsson, A., 2022. Rapid shifting of a deep magmatic source at
Fagradalsfjall volcano, Iceland. Nature 609. https://doi.org/10.1038/s41586-022-04981-x

M. Kahl, E.J.F. Mutch, J. Maclennan, D.J. Morgan, F. Couperthwaite, E. Bali, T. Thordarson,
G.H. Guðfinnsson, R. Walshaw, I. Buisman, S. Buhre, Q.H.A. van der Meer, A.
Caracciolo, E.W. Marshall, M.B. Rasmussen, C.R. Gallagher, W.M. Moreland, Á.
Höskuldsson, R.A. Askew; Deep magma mobilization years before the 2021 CE
Fagradalsfjall eruption, Iceland. Geology 2022. 51 (2): 184–188. doi:  https://doi.org/10.1130/G50340.1

Caracciolo, A., Halldórsson, S.A., Bali, E., Marshall, E.W., Jeon, H., Whitehouse, M.J.,
Barnes, J.D., Guðfinnsson, G.H., Kahl, M., Hartley, M.E., 2022. Oxygen isotope
evidence for progressively assimilating trans-crustal magma plumbing systems in
Iceland. Geology. https://doi.org/10.1130/g49874.1

Presentations at International Conferences (for brevity, PI presentations only):
Marshall, Edward; Rasmussen, Maja; Halldorsson, Saemundur; Matthews, Simon; Ranta,
Eemu; Sigmarsson, Olgeir; Robin, Jóhann; Barnes, Jaime; Bali, Enikö; Caracciolo,
Alberto (2022) An overview of the geochemistry and petrology of the mantle-sourced
Fagradalsfjall eruption, Iceland. EGU General Assembly Conference Abstracts

Marshall, E. W., Rasmussen, M. B., Halldorsson, S. A., Matthews, S., Ranta,
E., Sigmarsson, O., et al. (2021). Rapid geochemical evolution of the mantle-sourced
Fagradalsfjall eruption, Iceland. AGU Fall Meeting, New Orleans, USA.

Edward Marshall, Saemundur Halldorsson, Eemu Ranta, Alberto Caracciolo, Eniko Bali,
Heejin Jeon, Martin Whitehouse, Andri Stefansson (2020) The boron isotope systematics
of Icelandic basalts and melt inclusions. 2020 Goldschmidt Conference.

Edward W Marshall, Saemundur A Halldorsson, Eemu Ranta, Martin J Whitehouse, Andri
Stefansson (2019) The boron isotope systematics of Icelandic basalts and their
constraints on the Icelandic mantle source. 2019 AGU Fall Meeting.

Heiti verkefnis: Li og B samsætur í íslensku storkubergi og jarðhitavökva / Li and B isotope variability in Icelandic lavas and hydrothermal systems
Verkefnisstjóri: Edward W. Marshall IV, Háskóla Íslands
Tegund styrks: Nýdoktorsstyrkur
Styrktímabil: 2019-2021
Fjárhæð styrks kr. 29.925.000
Tilvísunarnúmer Rannís: 195638